A kitchen machine of the kind mentioned in the opening paragraph is known from European Patent 0 158 032 and comprises a locking device which is mechanically coupled to a switch button for operating the electric motor. The locking device comprises a bush which is journalled in the housing of the kitchen machine and is provided with two incisions made substantially diagonally opposite one another. The bush is provided with a concentric disc which has a number of teeth near a circumference. The switch button is also journalled in the housing and is provided with a C-shaped rim at a lower side. When the bowl with the lid are not placed on the housing correctly, the bush will be in such a position that the C-shaped rim of the switch button hits against the bush upon rotation of the switch button, and the electric motor cannot be switched on. It is prevented in this manner that the electric motor can be switched on while the bowl and the lid are not positioned correctly on the housing.
The lid of the bowl comprises a tongue which is also provided with a number of teeth near a circumference. If the bowl with the lid is placed correctly on the housing, the tongue is rotated into a recess of the housing, whereby the teeth of the tongue engage with the teeth of the bush, and the bush is rotated into a position in which the incisions of the bush are present opposite the ends of the C-shaped edge of the switch button. The electric motor can now be switched on by rotation of the switch button, the C-shaped rim entering the incisions of the bush. After rotation of the switch button, the bush cannot be rotated anymore, so that the lid of the bowl is locked. It is prevented thereby that the lid can be removed during rotation of the electric motor and that the user can injure himself with the rotating tool.
A disadvantage of the known kitchen machine is that the lid of the bowl is released already by the locking device the moment the electric motor is switched off with the switch button. The user of the kitchen machine may thus remove the lid from the bowl immediately after switching-off of the electric motor. The user can still injure himself with the tool then, because the electric motor and the tool driven thereby continue rotating for a short time after switching-off of the electric motor, which time depends on the mass inertia moments of the electric motor and the tool and the frictional forces experienced by the electric motor and the tool.